1. Field of the Invention
This invention relates to a punch and stripper assembly for use in press-type of machine tools.
2. Prior Art
It has long been the practice, which still continues, to utilize a stripping spring in a punch and stripper assembly where the stripper spring is permitted to expand to its free length after a power stroke. Such practice causes the spring to be stressed from zero to a maximum, which minimizes spring life. Further, the length of the assembly cannot be absolutely controlled because of the inherent differences in the lengths of the springs of a production lot, and also because the free length of springs tends to change with flexing, particularly when a spring is new. When punch and stripper assemblies are utilized in contemporary high performance equipment, the tooling length or envelope must be controlled. An example of a punching device having a punch and stripper assembly of such prior type is shown in U.S. Pat. No. 2,953,051.
To provide a preload on a stripping spring is known, as shown in U.S. Pat. No. 3,079,824. However, the prior types of punch and stripper assemblies that do have a preload on the stripping spring are so constructed that special tooling is needed to order to put the assembly together or to disassemble it for service, such as needed to replace a broken spring.